Asthma is an important disease that afflicts 5% of the general population. Atopic asthma is caused by biased-T helper 2 (Th2) responses to allergens. In a mouse model, mice primed intratracheally with Ag-pulsed dendritic cells and challenged with Ag developed airway hyperresponsiveness, and lung eosinophilia and inflammation. Lungs have a more Th2-biased environment and primed T cells seem to divide faster in the lungs than lymph nodes in Ag-challenged mice, although the lymph node is believed to be the site of T cell activation and development. In this study, lung DC have been found to be composed of multiple subset. Studies on DC migration suggest that secondary lymphoid chemokine (SLC/CCL21) may be a key chemokine for DC migration to draining LN. In the lung but not lymph nodes of lung-immunized mice, large numbers of interferon-gamma-producing CD8+ T cells (Tc1) were present, resulting in a more Th2-baised environment in the lungs. These results support the hypothesis that: "a DC subset that presents antigen in lungs and mediates a Th2-biased response occurs in lungs. For T lymphocyte and DC migration to lymph nodes, SLC is a major mediator. Because Th1 and Tc1 cell numbers are very low in the inflammatory lungs, activated T cells readily develop into Th2 cells." In this proposal, experiments are designed to support this hypothesis. The aims consist of: (1) the isolation and functional studies of DC subsets in lungs; (2) the studies of CCR7/SLC interaction as a key chemokine receptor/chemokine interaction for lung DC and T cell migration to lymph nodes. The roles of other important candidate chemokine receptors such as CCR2 in mediating DC migration will also be examined; and (3) the studies of the migration of IFN-gamma-producing CD8+ T cells away from lungs during asthma pathogenesis. These studies will clarify the roles of DC and CD8+ T cells in the biased-Th2 lung response in asthma and provide a novel mechanism for Th2-biased responses during asthma pathogenesis. The results may provide additional therapeutic strategies in asthma by the interference of SLC functions and by regulating the migration of DC, Th1, and IFN-gamma-producing CD8+ T cells.